The embryo's relationship with its surroundings is not fully understood

Mice born from embryos cultured in the laboratory showed behavioural differences from normal mice, according to a study.

The mice showed signs of more anxiety - and performed worse in memory tests.

The finding, published in the Proceedings of the National Academy of Sciences, suggests the lab dish environment may have an effect.

The University of Pennsylvania researchers said human IVF specialists should take note of the findings.

They stressed it was too early to suggest the same could be happening to human IVF embryos.

However, they said it might be wise to minimise the effects of the culture solution on the embryo by avoiding undue delay between fertilisation and implantation during IVF.

Modern trends

After sperm and eggs are combined during IVF, any resulting embryos are kept for a few days in a solution of nutrients and other chemicals to grow until they are ready to be implanted into the womb.

Modern trends in IVF have involved keeping the embryo in culture a little longer to pick the best candidates for successful implantation.

This cocktail offers the embryos what it needs to survive and develop - but is not a precise match for the natural chemicals found in the reproductive tract.

The results highlight the need for further research to optimise culture condition for human embryos

Dr Richard Schultz, University of Pennsylvania

Scientists have long suspected that the environment even in the first few days after conception might have an effect on the way it develops.

In particular, certain genes may be "misexpressed" in response to the makeup of the culture fluid.

During standard tests to test their behaviour and learning, the male mice developed from cultured embryos showed signs of behavioural changes - such as spending more time in open spaces, and showed small but statistically significant decreases in memory over normally conceived mice.

It is unclear whether human genes can be misexpressed in the same way when embryos are placed in culture.

Professor Richard Schultz, who led the study: "Our results are not directly applicable to children conceived through assisted reproductive technology.

"Nevertheless, the results highlight the need for further research to optimise culture condition for human embryos."

Culture medium

His colleague, Professor Ted Abel, said there should be a precautionary approach to keeping embryos in culture.

"Decreasing the length of time between fertilisation and implantation and further refining the composition of the culture medium are two ways that may mitigate risk."

Professor Tom Fleming, from the University of Southampton, told BBC News Online: "We don't know if this is actually relevant to humans, as there are a number of differences between animal and human embryos.

"There is an effort to mimic the reproductive tract environment - but we are a little bit behind in understanding that.

"It would be wrong to cause a scare over this, but it is probably a good idea to limit the length of time an embryo is in culture."